If you are on an ISP gateway, the default features can be rough on smart home gear... Band steering on by default, nightly self healing, and client isolation on guest can all break the Alexa path. Make a separate 2.4 only SSID for IoT and confirm that client isolation is off so your Echo and the plugs can see each other. Keep it plain WPA2 AES and fixed channel. If the gateway insists on doing auto optimization at night, turn that schedule off or move the IoT SSID to an attached access point or extender that you control. Stability over speed here.
